1. Field of the Invention
The present invention relates to a detent escapement for a timepiece and a mechanical timepiece using the same.
2. Description of the Related Art
In the related art, a detent escapement is known as an escapement for daily rate of a mechanical timepiece. These kinds of escapement mechanisms are generally classified into a spring detent escapement and a pivoted detent escapement (for example, refer to JP-A-2010-181223, JP-T-2009-510425, and pages 39 to 47, “The Practical Watch Escapement”, Premier Print Limited, 1994 (First Edition), written by George Daniel).
Hereinafter, a basic configuration of each detent escapement will be described.
FIG. 16 is a perspective view showing an example of the spring detent escapement of the related art.
As shown in FIG. 16, the spring detent escapement 300 includes an escape wheel 301, a balance 303 that is freely oscillated about a balance staff 302 being a rotation axis, and a detent lever 304. The balance 303 includes an impulse jewel 305 that can contact a wheel tooth 301a of the escape wheel 301, and an unlocking stone 306 that can contact a one-side actuating spring (passing spring) 309 which is attached to the detent lever 304.
The detent lever 304 is fixed via a balance spring 307 which is installed at a base end thereof. The balance spring 307 supports the detent lever 304 so that the detent lever 304 approaches to and separates from the escape wheel 301, and biases the detent lever 304 to be returned to the original position. That is, the detent lever 304 is constituted being capable of approaching to and separating from the escape wheel 301 with the base end of the balance spring 307 as a fulcrum 304a. 
In addition, a locking stone 308, which can contact the wheel tooth 301a of the escape wheel 301, is installed to the detent lever 304. Moreover, the base end of the one-side actuating spring 309 is fixed to the base end side of the detent lever 304. The one-side actuating spring 309 is formed along the longitudinal direction of the detent lever 304 so that the tip of the one-side actuating spring 309 is slightly more protruded than that of the detent lever 304. That is, the one-side actuating spring 309 is formed so as to be along a straight line which passes through the balance staff 302 of the balance 303 and the fulcrum 304a of the detent lever 304. In addition, the tip of the one-side actuating spring 309 comes into contact with the unlocking stone 306 of the balance 303.
According to the above-described configuration, if the unlocking stone 306 is rotated toward the direction of an arrow CCW30 (a counterclockwise direction in FIG. 16) due to the fact that the balance 303 is freely oscillated, the detent lever 304 is pressed through the one-side actuating spring 309. Thereby, the locking stone 308, which comes into contact with the wheel tooth 301a of the escape wheel 301, is separated from the wheel tooth 301a, and the engagement between the escape wheel 301 and the detent lever 304 is released. Therefore, the escape wheel 301 is rotated by one tooth.
While the escape wheel 301 is rotated by one tooth, a bias force of the balance spring 307 acts on the detent lever 304, and the detent lever 304 is returned to the original position. Therefore, the locking stone 308 comes into contact with the wheel tooth 301a of the escape wheel 301 again. That is, the escape wheel 301 is engaged with the detent lever 304, and the rotation of the escape wheel 301 is stopped.
On the other hand, if the unlocking stone 306 reverses due to the free oscillation of the balance 303 and is rotated toward a direction of an arrow CW30 (a clockwise direction in FIG. 16), by the unlocking stone 306, the one-side actuating spring 309 is pressed toward the direction in which the one-side actuating spring 309 is separated from the detent lever 304. At this time, the detent lever 304 comes to be in the stopped state while the one-side actuating spring 309 is elastically deformed. After the unlocking stone 306 is separated from the one-side actuating spring 309, the one-side actuating spring 309 which is pressed to the unlocking stone 306 is returned to the original position by a restoration force of the one-side actuating spring 309 itself.
That is, when the unlocking stone 306 is rotated toward the direction of the arrow CCW30 and the detent lever 304 is pressed via the one-side actuating spring 309, the one-side actuating spring 309 does not perform any operation. On the other hand, if the unlocking stone 306 is rotated toward the direction of the arrow CW30, the one-side actuating spring 309 is elastically deformed and operated.
In addition, due the fact that the operation is repeatedly performed, a train wheel of the mechanical timepiece is driven at a constant speed.
FIG. 17 is a perspective view showing an example of the pivoted detent escapement of the related art. In addition, the same aspects as the spring detent escapement 300 of FIG. 16 are described with denoting the same reference numbers.
As shown in FIG. 17, the pivoted detent escapement 400 includes the escape wheel 301, a balance 403 which is freely oscillated about the balance staff 302, and a detent lever 404. Here, the difference between the pivoted detent escapement 400 and the spring detent escapement 300 is that the basing means for returning the detent lever to the original position are different to each other.
That is, the detent lever 404 of the pivoted detent escapement 400 is rotatably supported via the rotation axis 410, and therefore, the detent lever 404 can approach to and separate from the escape wheel 301. In addition, a balance spring 407 installed to the detent lever 404 is constituted by a coil spring so as to enclose a rotation axis 410, and biases the detent lever 404 to be returned to the original position.
In addition, in the detent lever 404, the base end of the one-side actuating spring 409 is fixed to a straight line P100 which is approximately perpendicular to the longitudinal direction of the detent lever 404 and passes through the rotation axis 410. The one-side actuating spring 409 is formed so as to be along the longitudinal direction of the detent lever 404, that is, the straight line which passes through the balance staff 302 of the balance 403 and the rotation axis 410 of the detent lever 404. The tip of the one-side actuating spring comes into contact with the unlocking stone 306 of the balance 403.
According to the configuration, due to the fact that the balance 403 is freely oscillated, if the unlocking stone 306 is rotated in the direction of an arrow CCW31 (a counterclockwise direction in FIG. 17) or in the direction of an arrow CW31 (a clockwise direction in FIG. 17), the one-side actuating spring 409 is operated or not operated at all according to the rotation. In addition, the locking stone 308 of the detent lever 404 is engaged with or separated from the wheel tooth 301a of the escape wheel 301. Therefore, the train wheel of the mechanical timepiece is driven at a constant speed.
However, in the above-described related art, when the one-side actuating springs 309 and 409 are operated, the unlocking stone 306 is rotated against the spring force. Therefore, energy loss with respect to the free oscillation of the balances 303 and 403 occurs. In addition, the positions of the detent levers 304 and 404 and the one-side actuating springs 309 and 409 with respect to the unlocking stone 306 influences the operation of the escape wheel 301.
That is, for example, if the contact area between the unlocking stone 306 and the one-side actuating springs 309 and 409 is small, variations toward the direction in which the one-side actuating springs 309 and 409 are separated from the escape wheel 301 are as small as the decreased contact area. Therefore, the separation movement of the locking stone s 308 and 308 of the detent levers 304 and 404 with respect to the wheel tooth 301a of the escape wheel 301 is difficult to normally perform, and the escape wheel 301 cannot be rotated for each tooth.
In addition, if the tip positions of the detent levers 304 and 404 are too close to the balances 303 and 403, there is a concern that the unlocking stone 306 and the detent levers 304 and 404 may come into contact with each other. In this case, free oscillation of the balances 303 and 403 are impeded by the detent levers 304 and 404, and the balances 303 and 403 cannot be normally operated. As a result, the escape wheel 301 is not normally operated.
Therefore, it is necessary to position the detent levers 304 and 404 and the one-side actuating springs 309 and 409 with respect to the unlocking stone 306 with high accuracy. Thus, the position adjustment operation of the detent levers 304 and 404 and the one-side actuating springs 309 and 409 is troublesome.